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ANIMAL PRODUCTION |
Department of Animal Sciences, The Ohio State University, Wooster 44691
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
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Key Words: Age • Beef Cattle • Corn Processing • Feedlot • Forage
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Introduction |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
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; Turgeon et al., 1983) and feedlot performance (Cole et al., 1976a; Zinn et al., 2002), although results have not been consistent. In extensive reviews, Owens et al. (1986, 1997) reported that corn processing (grinding) did not improve starch digestibility or feedlot performance. Several factors affect corn digestibility; however, their importance is not completely understood (Huntington, 1997).
Feedlot performance trials with weanling steers have failed to prove advantages for rolled vs. whole high-moisture corn (Loerch and Fluharty, 1998), perhaps because chewing capacity is greater in younger cattle (Nicholson et al., 1971). To our knowledge, there is no information available about the possible interaction between cattle age and the digestibility of whole corn.
There are limited and conflicting data in the literature (Cole et al., 1976b; Loerch and Fluharty, 1998) regarding the effects of forage level on the digestibility of whole corn. High forage levels in the diet can decrease metabolic disorders, but they could also increase passage rate (Cole et al., 1976b) and may lower the extent of whole corn digestion (Teeter et al., 1981).
The effects of cattle age and forage level on corn digestibility have not been adequately determined. Three experiments were conducted to evaluate the effects of cattle age, forage level, and corn processing on diet digestibility and feedlot performance.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
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).
Experiment 1
A digestibility trial was conducted with 16 crossbred steers in a completely randomized experimental design with a 2 x 2 factorial arrangement of treatments to determine the effects of animal age and corn processing on diet digestibility. Two animal age categories were used in this experiment. Eight weaned steers (254 ± 20 kg of average BW) were classified as weanlings, and eight steers (477 ± 29 kg BW) were classified as yearlings.
Steers were purchased at a feeder calf sale and their exact age and background were unknown; they were classified as weanlings or yearlings based on BW. Upon arrival at The Ohio State University feedlot in Wooster, steers were vaccinated for protection against infectious bovine rhinotracheitis, parainfluenza-3, Haemophilus somnus, Pasteurella and Clostridia (Quadraplex, Somnugen 2P, and Dybelon, respectively; Bioceutic, St. Joseph, MO), and dewormed with Ivomec pouron (Merck, Rahway, NJ). Steers were revaccinated 14 d later.
The animals were placed in individual pens in a totally enclosed feedlot barn, with slatted concrete floors and metal gates. Pens were 2.6 m x 1.5 m, giving each steer 3.9 m2 of floor space. Steers were fed once daily at 0800, and refusals were weighed, recorded, and discarded daily before feeding. A 30-d period was allowed for adaptation to the feedlot and to gradually increase grain content of the diet to 80% corn.
After the 30-d receiving period, animals were fed a diet comprising (DM basis) 80% corn, 8% forage, and 12% supplement (Table 1). For both animal age categories, corn grain was fed either ground or whole. Thus, four treatment groups were tested: weanling, whole corn; weanling, ground corn; yearling, whole corn; and yearling, ground corn, with four animals in each treatment group.
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The experimental period consisted of 13 d, with 12 d for adjustment to the experimental diets, followed by a 24-h total collection of feces. Feces were recovered using fecal collection bags. Bags were held in position by straps attached to a harness located on the animal’s back.
At the end of the 24-h collection, weight of total fecal output was recorded and fecal samples were taken and frozen for future analysis. Feed and refusal samples were taken on d 12 and 13, respectively, to determine feed intake. These samples also were frozen for future analysis.
The number of whole corn kernels fed, refused, and those that appeared in feces of cattle fed whole corn was counted. Samples with 10% of the total weight of feed, refusals, and feces were used for the counting. When feed refusals were less than 1 kg, corn kernels were counted in the total feed refusal.
Experiment 2
One hundred eighty Angus crossbred steers (310 ± 40 kg BW; 8 to 9 mo of age) were used to determine the effects of forage level and grain processing method on feedlot performance and carcass characteristics. A randomized complete block experimental design with a 2 x 3 factorial arrangement of treatments was used.
Steers were blocked into four weight groups and allotted within weight groups to six pens, with seven or eight steers per pen (24 pens total). Treatments were assigned randomly to pens within a weight block. Main effects were two forage levels and three corn processing treatments.
The six treatment combinations investigated were high-forage (18.2% corn silage in the diet), cracked corn (HFCC); high-forage shifting corn (steers fed whole corn for approximately the first half of the trial, then switched to cracked corn for the rest of the trial; HFSC); high-forage, whole corn (HFWC); low-forage (5.2% corn silage), cracked corn (LFCC); low-forage, shifting corn (LFSC); and low-forage, whole corn (LFWC). Composition of diets is presented in Table 2.
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The experiment was conducted at The Ohio State University feedlot in Wooster. Pens (5.4 m x 5.4 m) were constructed of metal gates and cable. They had concrete slatted floors, and were located in an open-sided barn.
Before starting the trial, all steers received a common 65% concentrate diet for 60 d. Steers were vaccinated as described in Exp. 1 and were treated with Dectomax (Pfizer, Exton, PA) for internal and external parasites before arrival at the feedlot.
For the HFSC and LFSC treatments, the switch to cracked corn occurred on different dates for each block because the blocks had different initial weights and were predicted to have different days on feed. Animals in pens allotted to the shifting corn treatments (HFSC, LFSC) were switched from whole corn to cracked corn diets when steers within each weight block were predicted to be 84 d from their projected slaughter date.
The shift in corn processing was accomplished by switching from whole to cracked corn in one day, decreasing feed offered by 10% for 2 d, and then continuing with normal feed bunk management.
All steers were implanted with Synovex-S (20 mg of estradiol benzoate, 200 mg of progesterone; Fort Dodge Animal Health, Overland Park, KS) on d 1 of the experiment. All steers within a block were reimplanted with Synovex-S on the date corn was switched from whole to cracked for the HFSC and LFSC treatments in that block.
Feed was offered daily beginning at 0800. Approximately 60 cm of bunk space was available per animal. Feed refusals were weighed, recorded, and discarded daily. Fresh water was available at all times. Feed samples were analyzed weekly for DM to allow determination of DMI. Composite feed samples were dried in a forced-air oven at 55°C and stored for future analysis.
Initial and final BW was determined using the average BW measured on two consecutive days. Steers also were weighed at 28-d intervals during the trial. Steers were weighed before feeding at 0800 and were not withheld from feed or water.
Animals within a weight block were slaughtered when mean backfat of animals within the block was estimated to be 1.4 cm. Hot carcass weight, fat thickness, LM area, and percentage of kidney, pelvic, and heart fat were determined by Ohio State University personnel. Carcass yield grade was calculated (USDA, 1997). Quality grade and marbling score were determined by a USDA official. Carcass characteristics were measured after a 48-h chill.
Experiment 3
Sixteen crossbred steers (350 ± 27 kg) were used in a completely randomized experimental design with a 2 x 2 factorial arrangement of treatments to determine the effects of forage level and grain processing on diet digestibility. Steers were allotted to one of the diets (HFWC, HFCC, LFWC or LFCC) used in Exp. 2 (Table 2
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Corn was processed as described for Exp. 2. Median particle size was approximately 2.83 mm, with 80.3% of the particles between 1.4 and 4.0 mm. Corn silage was harvested as described in Exp. 2, and average DM at time of feeding was 35%.
Vaccination and deworming protocols, individual animal penning, and feeding procedures were as described in Exp. 1. The experimental period was 21 d in length. Days 1 through 13 were used for adjustment to the diets, and on d 14, a 24-h total collection of feces was performed. Between d 15 and 20, steers remained on the same diet, and on d 21 a second 24-h collection of total feces was done.
Feces were recovered using fecal collection bags, as described previously. At the end of each 24-h collection, weight of total feces excreted was recorded, and two fecal samples (20% of total fresh weight each) were taken and frozen for future analysis. Feed and refusal samples were taken on d 12 and 19 of the experimental period, and were frozen.
For steers fed the whole corn treatments, one of the frozen fecal samples from each collection was thawed, and the d-14 and -21 samples were composited for each animal. The number of whole corn kernels recovered in feces was counted. The number of corn kernels in feed and refusals was determined by counting the number of corn kernels in 10% of the feed offered and refused. When feed refusals were less than a kilogram, corn kernels were counted in the total feed refusal.
Feed, refusals and fecal samples were composited over sampling days for each animal, freeze-dried, and ground to pass a 1-mm screen before analysis. Corn kernels recovered from feces of each animal also were freeze-dried, ground, and stored for future analyses.
Analyses and Calculations
Feed samples of Exp. 2. and samples of feed, refusals, feces, and corn kernels recovered in feces of Exp. 1 and 3 were analyzed for DM, OM (AOAC, 1984), N (FP-2000 N-analyzer, Leco Corp., St. Joseph, MI), and starch (Fleming and Reichert, 1980). For Exp. 1 and 3, feed, refusals, and fecal samples also were analyzed for NDF and ADF (Van Soest et al., 1991). Nutrient digestibility was determined by the difference between nutrient intake 24 h before fecal collection and the nutrient output in feces divided by intake.
Statistical Analyses
In Exp. 1 and 3, the DM, OM, CP, starch, NDF and ADF digestibility data were analyzed using the GLM procedures of SAS (SAS Inst., Inc., Cary, NC) for a completely randomized experimental design with a 2 x 2 factorial arrangement of treatments. For Exp. 1, the model included cattle age, corn processing method, and the cattle age x corn processing method interaction. For Exp. 3 the model included forage level, corn processing method, and the forage level x corn processing method interaction. Residual mean square was the error term and animal was the experimental unit. The starch content of feces (fecal starch as a percentage of fecal DM) and starch and DM digestibility of the diet were additionally analyzed using the CORR and REG procedures of SAS to determine the relationship between fecal starch and digestibility.
In Exp. 2, data were analyzed using GLM procedures of SAS for a randomized blocked design with a 2 x 3 factorial arrangement of treatments. The model included the effects of forage level, corn processing method, the forage level x corn processing method interaction, and block. Treatment means were compared using the PDIFF statement of SAS, protected by a significant (P < 0.05) F-value. Pen was the experimental unit for all analyses.
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Results and Discussion |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
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) and discussed. Neither cattle age nor corn processing affected diet DM, OM, starch, CP, NDF and ADF digestibility (P > 0.10).
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; Morgan and Campling, 1978). When whole corn is fed, chewing capacity is important for DM and starch digestion because ruminal fermentation does not begin until the corn kernel cuticle is disrupted (Kotarski et al., 1992). This disruption can be achieved either mechanically (grain processing) or through chewing during the eating and rumination processes (Beauchemin et al., 1994; McAllister et al., 1994). The difference in cattle age (weanling vs. yearling steers) may not have been great enough to allow the expression of chewing capacity differences, or chewing capacity of both weanling and yearling steers fed whole shelled corn was sufficient to allow similar starch digestibility to that of steers fed ground corn (Hooper and Welch, 1982; Bae et al., 1983).
Starch content of feces is used in commercial feedlots to evaluate starch digestibility of the diet (Zinn et al., 2002). In this experiment, cattle age did not affect (P = 0.79) fecal starch concentration. Feeding whole corn resulted in a 44% increase (P = 0.01) in fecal starch concentration compared with feeding ground corn. Despite this, differences in starch digestibility due to corn processing were minimal (less than 2%) and not significant (P = 0.33).
Regression analysis was performed to determine the relationship between fecal starch content and starch digestibility for each dietary treatment. Slopes of the regressions did not differ among treatments (P > 0.10); therefore, the data were pooled. The resulting regression equation was: % starch digestion = 101.0 – 0.48 (% fecal starch; r2 = 0.57; P = 0.001). Caution should be used when only starch content of feces is used to evaluate the quality of diets. To determine the digestibility of a diet, one must know not only the concentration of the nutrient in feed and feces, but also the amount of feed consumed and feces excreted (Merchen, 1988). For instance, increasing dietary fiber would increase fecal DM output, thereby decreasing fecal starch concentration without affecting starch digestibility.
Although the appearance of whole corn kernels in feces suggests that digestion is inefficient, there are limited data in the literature quantifying the importance of this phenomenon for starch utilization (Driedger and Loerch, 1999). In the present experiment, the number of corn kernels ingested and excreted did not differ (P > 0.10) between cattle age groups (Table 4). Pooled corn kernel disappearance was 92%, slightly above the 88% reported by Driedger and Loerch (1999) for nonlactating Holstein cows, which supports the concept that whole shelled corn diets can be properly digested by steers fed high-concentrate diets.
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). Experiment 2 was designed to evaluate the hypothesis that cattle fed whole corn would perform better with low-forage diets, whereas cattle fed high-forage diets would perform better when corn was cracked. Nonetheless, interactions between forage level and corn processing were not detected (P > 0.10) for overall feedlot performance and carcass characteristics, giving no support for our hypothesis.
An interaction occurred (P = 0.06) between forage level and grain processing treatments for ADG during Phase 1 of the trial (Table 5). For the low-forage diets, cattle fed whole corn gained 6% faster than those fed ground corn. For the high-forage diets, feeding whole corn did not increase ADG. This response was not evident during Phase 2, and total ADG for the trial was not affected (P = 0.53) by forage level or grain processing treatment. Greater ADG by cattle fed the LFWC diet was not expected and this effect may be spurious. Cattle fed LFSC also were fed whole corn during Phase 1 and their growth rate was similar to that of cattle fed cracked corn.
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; Zinn et al., 2002) because it increases the net energy content of the diet (NRC, 1996). However, in a review of published experiments, Owens et al. (1997) reported similar ADG by steers fed cracked, steam-flaked, or whole corn. Improvements in ruminal starch fermentation with corn processing can be offset by excessive rates of acid production in the rumen and subclinical acidosis (Fulton et al., 1979a,b), resulting in similar feedlot performance compared with whole corn diets. Starch escaping fermentation in the rumen can be digested in the small and large intestine, and total-tract starch digestibility has been reported to be similar between cracked and whole corn (Owens et al., 1986). Furthermore, starch fermentation rate is slower with whole corn diets, decreasing the risk of digestive disorders, which is reflected in growth rates comparable to those with processed corn diets.
An interaction between forage level and grain processing treatment occurred (P = 0.02) for daily DMI during the total trial. For the high-forage diets, steers fed cracked corn had 7% greater DMI than those fed whole corn, whereas for the low-forage diets grain processing did not affect DMI. It was expected that whole corn treatments would have higher DMI to compensate for their lower energy concentration. When ruminants are fed high-energy diets and gut fill does not limit intake, they typically adjust their DMI to equalize energy intake (Conrad et al., 1964). Unexpectedly, the opposite effect was detected.
No interactions between forage level and corn processing were detected (P > 0.10) for feed efficiency. During Phase 1, feed efficiency was higher (P = 0.01) for low- than for high-forage-fed groups (240 vs. 227 g of gain/kg of feed, respectively). During Phase 2, feed efficiency was not affected (P = 0.53) by forage level, but feed efficiency for steers fed the low-forage diets remained greater (P = 0.02) than that of steers fed the high-forage diets for the total feeding period (197 vs. 190 g of gain/kg of feed, respectively).
Higher feed efficiency in low-forage diets can be expected due to increased energy concentration with decreasing forage level. Forage is included in feedlot diets to improve ruminal health status. The inclusion of 5.2% corn silage in the diet (DM basis) likely provided adequate forage to maintain good ruminal health (Koenig et al., 2003); thus, steers were able to take advantage of the higher energy concentration of this diet.
Feed efficiency was higher during Phase 1 for whole than for cracked corn diets (240 vs. 229 g of gain/kg of feed; P = 0.05). In a summary of published research, Owens et al. (1997) reported that diets containing whole corn resulted in higher feed efficiencies than those containing dry rolled corn, but were lower than those observed with diets containing steam-rolled corn. Interestingly, these authors attributed the greater efficiency reported for whole corn diets to the low forage levels typically fed when whole corn is used in feedlot diets. In this experiment, overall feed efficiency for the total trial was similar for cattle fed whole vs. those fed cracked corn.
The shifting corn treatment was intended to provide a slower fermentation rate with whole corn during the initial phase of the feeding period, decreasing the risk for acidosis when steers are more susceptible to digestive upsets, and then to provide a higher energy density with cracked corn after the initial feeding period. This strategy did not improve ADG or G:F compared with feeding corn whole or cracked throughout the feeding period.
An apparent interaction between days fed and corn-processing method for growth rate and feed efficiency was observed. Cattle performance responses to grain processing were not consistent among the four weight blocks. Due to insufficient replication, the days fed x corn processing interaction could not be tested using GLM procedures (SAS Version 8) for a randomized block design. Thus, the interaction of days on feed (DOF) and corn processing on ADG and G:F was analyzed statistically using the Mixed procedures of SAS Version 8. Pen was the experimental unit. Because steers on the shifting corn treatments consumed both cracked and whole corn, only data from the cracked and whole corn treatments were included in the analysis. The model included forage level and corn processing as main effects, days fed as a continuous variable, and the forage level x corn processing, forage level x days fed, corn processing x days fed, forage level x corn processing x days fed interactions.
Days fed x corn processing interactions for growth rate (P = 0.07) and feed efficiency (P = 0.01) were detected (Figures 1 and 2, respectively). For cattle fed cracked corn, maximum growth rate was observed in the heaviest weight block (1.87 kg/d at 129 DOF), and growth rate was progressively slower for the lighter weight blocks (1.60 kg/d at 185 DOF). Feed efficiency remained mostly unchanged among weight block groups for cattle fed cracked corn diets (191 vs. 190 g of gain/kg of feed for 129 and 190 DOF, respectively). Conversely, when whole corn was fed, growth rate remained mostly unchanged among weight blocks (1.76 vs. 1.64 kg/d at 122 and 192 DOF, respectively), but feed efficiency was greater for lighter weight blocks that were on feed for more days (188 vs. 207 g of gain/kg of feed at 122 and 192 DOF, respectively).
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Lack of a performance response to corn processing for cattle on feed for longer time periods may have been due to long-term, cumulative effects of increased starch fermentation rate (Huntington, 1997; Beauchemin et al., 2003). Subacute acidosis (Fulton et al., 1979a,b) and decreasing integrity of ruminal epithelial tissue (Bartle and Preston, 1992) may have contributed to the response observed. The interaction of time on feed and grain processing may explain part of the conflicting responses to grain processing previously reported in the literature. Further research specifically designed to test the interactions between corn processing and days on feed is warranted.
Forage level and corn processing effects on carcass characteristics are presented in Table 6. Low forage-fed cattle had heavier (P = 0.04) HCW, reflecting the higher energy concentration of their diets. Grain processing affected (P = 0.01) marbling score. When averaged over forage level, marbling scores were 376, 400, and 347 points for cattle fed cracked corn, shift corn, and whole corn, respectively. However, this effect on marbling score did not result in dietary treatment effects (P > 0.10) for percentage of carcasses grading Select, or percentage of carcasses grading above low Choice. In addition, processing corn did not improve yield grades. The number of cattle marketed through quality and yield grids has increased dramatically during recent years (USDA, 2003). Considering that the most common standards to receive price premiums and avoid discounts are quality grades of at least Choice, and a yield grade not greater than 4, it may be concluded that feeding whole corn does not diminish the carcass value of the animal.
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). Starch digestion was not influenced by forage level or corn processing (P > 0.10). There was a tendency for an interaction (P < 0.08) between forage level and corn processing for DM digestibility. For the high-forage diets, when corn was cracked, diet DM digestibility was lower than when corn was fed whole; for the low-forage diets, feeding cracked corn increased DM digestibility (83.3, 81.4, 80.2, and 83.1%, respectively, for HFWC, HFCC, LFWC, and LFCC). This interaction in DM digestibility may be attributed in part to the interaction (P = 0.07) between forage level and corn processing on NDF digestibility; HFWC had 12% higher NDF digestibility than LFWC, whereas this value was not different for cracked corn diets.
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). The combined effects of high forage and whole corn may lead to a better ruminal environment for fiber digestion, increasing NDF and DM digestibility in HFWC but not in LFWC diets.
Starch digestibility did not differ among treatments (P > 0.59). The lack of response in starch digestion to forage level is in agreement with results of McCullogh and Matsushima (1973), but in contrast to those of Cole et al. (1976a, b), who reported lower total gastrointestinal tract starch digestibility with the inclusion of 14 to 21% dietary forage. The forage levels investigated in the present trial were 5.2 and 18.2% corn silage on a DM basis. Forage source and particle size affect ruminal pH and digesta passage rate (Teeter et al., 1981; Krause and Combs, 2003). Further research is needed to determine whether the results we observed when corn silage served as the forage source would be repeatable for other forage sources.
Starch content of feces was not affected (P > 0.43) by forage level or corn processing. The correlation coefficient for starch content in feces and starch digestibility in whole (r = –0.98; P < 0.0001) and cracked (r = –0.95, P < 0.001) corn diets was similar to that reported by Zinn et al. (2000) for steam flaked corn (r = –0.95; P < 0.01).
Regression analysis was performed to determine the relationship between fecal starch content and starch digestibility for each dietary treatment. Slopes of the regressions did not differ among treatments (P > 0.10); therefore, the data were pooled. The resulting regression equation was: % starch digestion = 100.6 – 0.33 (% fecal starch; r2 = –0.92; P = < 0.01), which was similar to the equation calculated in Exp. 1.
The number of corn kernels ingested and excreted and corn kernel disappearance was not affected by forage level in the diet (Table 8). In both Exp. 1 and 3, less than 10% of the corn kernels fed were counted in feces. Additionally, the starch digestibility of whole corn diets was similar to that of processed corn diets. Thus, it can be concluded that the appearance of corn kernels in feces should not be the sole justification to process corn in feedlot diets.
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Implications |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
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Footnotes |
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2 Correspondence: 114 Gerlaugh Hall, OARDC, 1680 Madison Ave. (phone: 330-263-3900; fax: 330-263-3949; e-mail: loerch.1{at}osu.edu).
Received for publication February 27, 2004. Accepted for publication December 9, 2004.
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Literature Cited |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
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